The development of organic EL elements (OLEDs) has been advanced as candidates for next-generation display technology.
An organic EL element is a self light-emitting element, and the light emission area is defined by the opening region of an insulating layer called an edge cover. Since an entire organic EL element has a very thin film thickness of around 200 nm, an organic EL element cannot be formed in areas with large concavities and convexities such as contact holes for connecting pixel electrodes and circuit wiring line. Therefore, there is a problem that the reduction in light emission area due to contact holes becomes more substantial as the resolution becomes higher.
A contact hole needs to have an external size of about 10 μm due to the relationship between the contact resistances of the pixel electrodes and the circuit wiring line. Therefore, as the resolution of the panel becomes higher, the occupied area of contact holes in pixels becomes larger, and the reduction in the light emission area becomes more severe.
In addition, a contact hole is formed to have a steep wall surface. Therefore, when an organic EL element, which is a thin film, is formed inside a contact hole, there may be shorting between the upper and lower electrodes of the organic EL element, or pixel defects may arise without emitting light.
PTL 1 discloses technology for overcoming poor light emission of an organic EL element due to poor film formation of an organic EL material in a contact hole. In PLT 1, poor film formation of an organic EL material in an electrode hole of a pixel electrode can be prevented by forming a film of the organic EL material after forming a protection part by embedding an insulator in the electrode hole. This prevents current from being concentrated due to shorting between the upper electrode and lower electrode of the organic EL element and prevents poor light emission of the organic EL layer.